Special mechanisms of mutation are induced in bacteria and yeasts under growth-limiting stress causing genetic instability, and occasionally, adaptive mutations that may speed evolution. These stress-induced mutation mechanisms may provide superior models for genetic changes that promote aging, genetic instability underlying cancer formation, progression and acquisition of chemotherapy resistance, resistance of pathogens to host defenses and antibiotics, and possibly much of evolution generally. This proposal focuses on understanding the molecular mechanisms of stress-induced genetic instability in an E. coli model. Because the mechanism studied has common components with several other (less understood) mechanisms of stress-induced mutation, the results should provide an important general model.